package solution14;

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        while (sc.hasNext()) {
            int n = sc.nextInt();
            String[] strs = new String[n];
            for (int i = 0; i < n; i++) {
                strs[i] = sc.next();
            }

            System.out.println(new Solution().longestCommonPrefix(strs));
        }
    }
}
